As you hopefully noticed, those numbers do not add up to 100%. That extra 13% doesn't need to be included, although the more pizza the better. You can give a perfectly good presentation without it. You may be surprised to know that that's the design portion. Indeed, you do not need it; with solid content and wicked delivery, pretty slides are bonus material. (We all know that beautiful slides can really enhance a presentation. They're important, but not essential. We try not to bring this up frequently around the SquarePlanet designers...) That means that you should spend the vast majority of your time developing your content. What does that entail, exactly?
As we've posted before, great content is built with great stories. Your presentation can't just be facts, facts, facts, smile, facts, and a tacked-on invitation. That would be terribly dry. In the best case of that scenario, your audience would walk away well informed for a few hours before they forgot everything you said. In the worst case, they would feel like gouging out their eyes from boredom and hold you personally accountable for their feelings of existential doom. Neither of those situations are ideal. You want your audience to walk away feeling informed and moved. If you can get your audience to feel moved, it's more likely they'll remember your message and take action. And stories make people feel things.
Humans have a long history of storytelling, which works out for you and us because that means there are a variety of stories we can steal if we can't come up with our own. It's best to think of your own, though--it'll make you feel more passionate and invested, making your audience more passionate and invested. Maybe your material grew naturally from personal experience to begin with. If not, try to think of ways you can relate your material to your own life. If you can't think of any, go ahead and search the interwebs for inspiration and stories. Keep your beliefs and purpose in mind. Other tried and true resources for stories are books, magazines, and newspapers. Those things tend to be chock-full of stories. Once you've got a story that can be tied to your material, you can start adding in your facts (what we call the "know") because your audience has been properly primed to listen.
Two additional tools for making your facts relatable and understandable are metaphors and similes. Especially if your facts aren't particularly evocative, metaphors/similes offer a nice escape from convention. Metaphors and similes are also a good tool if you're trying to come up with an idea for a visual aid (not that you should care about visual aides at this point). Throughout this entire content development process, you should constantly be trying to simplify, so when you're thinking of a good metaphor/simile, make sure you're not using a difficult one lest you shoot yourself in the foot.
So those are the basics of content development: stories, feelings, facts, metaphors, and simplicity. That's a lot of stuff, and that's why it makes up 87% of presentations.